Lecture Notes: Water and Its Importance to Life

Introduction

• Focus on water's crucial role in life
• Topics: Emergent properties of water, solutions, concentrations, and acid-base chemistry
• Objectives:
  • Model and categorize molecular structure and functions related to living organisms
  • Describe molecular polarity and ionization
  • Relate molecular ionization to acids, bases, and pH

Origin of Water

• Water's origins: Earth’s hydrogen vs. icy space objects
• Water became prominent shortly after Earth’s formation, facilitating life
• Hydrothermal vents as the birthplace of life

Water's Properties

• Exists in three phases: solid, liquid, gas
• Only common substance in natural environment in all three states
• Phase diagram: Pressure vs. Temperature

Molecular Structure of Water

• Polar covalent bonds cause electrons to favor oxygen over hydrogen
• Leads to partial negative charge on oxygen, partial positive on hydrogen
• Results in water being a polar molecule

Hydrogen Bonds

• Weak bonds between water molecules
• Responsible for water's unique properties:
  • Cohesive behavior
  • Ability to moderate temperature
  • Expansion upon freezing
  • Versatility as a solvent

Cohesion and Adhesion

• Cohesion: Water molecules stick together, creating surface tension
• Adhesion: Attraction between water and other substances
• Important for water transport in plants

Temperature Moderation

• Oceans absorb and release heat, stabilizing temperature
• Specific heat capacity: Water has high specific heat due to hydrogen bonds

Density and Floating Ice

• Ice is less dense than liquid water due to structured hydrogen bonds
• Allows ecosystems to survive under ice

Water as a Solvent

• Polar nature makes water a versatile solvent
• Dissolves polar/ionic substances (hydrophilic)
• Does not dissolve nonpolar substances (hydrophobic)

Solutions and Concentrations

• Methods to calculate concentration: Molarity, percent solution, mass-to-volume ratio
• Molarity: Moles of solute per liter of solution
• Percent solution: Grams of solute per milliliters of solvent times 100

Acid-Base Chemistry

• Acids increase H+ concentration; bases decrease it
• Water can act as both acid and base (amphoteric)
• pH scale: Measures acidity/basicity (0-14 scale)
• Buffers help maintain stable pH in organisms

Conclusion

• Water is fundamental to life on Earth due to its unique properties
• Next topic: Carbon’s role in building biological molecules